About this task
Implementing a WSJPA ObjectCache object can improve the
performance of an application that has a set of data that is used
in a static, read-only method, like accessing basic persistent fields
and persisting unidirectional relationships to a read-only type. The
WSJPA ObjectCache is a non-distributed cache of read-only entities
that operates at the EntityManagerFactory level. These cached instances
are shared by all entity managers in the Java virtual
machine (JVM), but the instances are not managed by any. When the
feature is enabled, the ObjectCache object is examined before the
application accesses the OpenJPA DataCache object and database, and
persistent objects are loaded from the database and stored in the
OpenJPA object cache. In addition, the ObjectCache implementation
can be used with OpenJPA DataCache and QueryCache features for even
greater performance.
Be aware of the following conditions and
limitations:
- Include types that are strictly read-only from the application
point-of-view
- Passing a read-only type into the following operations results
in an UnsupportedOperationException error message:
- Passing a read-only Entity into EntityManager.merge(…).
- Passing a read-only Entity into EntityManager.persist(…).
- Passing a read-only Entity into EntityManager.remove(…).
- Calling a setter method on a read-only type that was returned
by the WebSphere JPA runtime might result in an UnsupportedOperationException
error message.
- Types that are included in the ObjectCache must not be eligible
to be cached in the OpenJPA DataCache. Do not intersect types that
are cacheable by the OpenJPA L2 cache (openjpa.DataCache); the ObjectCache
should not be confused with the second-level cache that is defined
by the JPA 2.0 specification. If types are intersected, an exception
might occur when the entity manager is created.
- Include only basic fields, or an exception might occur when the
entity manager is created.
- Passing a read-only Entity into EntityManager.contains(…) always
returns false, even if it was just returned from a find/query operation.
You can enable the object cache for a single JVM environment,
specify the types that are included in this cache, set its maximum
element size, and specify timeout values.
Supported configurations: The
preferred property name is wsjpa.ObjectCache, but openjpa.ObjectCache
is also a valid configuration.
sptcfg
What to do next
To enable automatic loading of the
entire ObjectCache when the first entity manager is created, follow
the steps in the
Pre-loading the WSJPA ObjectCache automatically topic.
In addition, you can read more about caching in the OpenJPA User Guide
for information about all caching extensions.